1. Field of the Invention
The present invention relates to N-substituted-isoxazolidine-3,5-diones as hypolipidemic agents and methods for their use in controlling hyperlipidemia in mammals. Specifically, the present invention is directed to methods for controlling hyperlipidemia by treating mammals, especially humans, with a class of hypolipidemic agents selected from isoxazolidine-3,5-diones.
2. Background of the Invention
Cholesterol is commonly found in all the tissues and blood of mammals, especially humans. Manufactured in the liver and other cells as a substrate for other steroids and bile acid and a component in membrane synthesis, cholesterol and its metabolic products are normal constituents of bile. As will be appreciated, many familiar foods contain cholesterol, with some containing more than others. Maintaining proper levels of cholesterol in the body has become an important factor in today's diet, since medical science has proven that certain afflictions such as hypothyroidism, diabetes and the intake of foods having a high cholesterol content may result in high levels of cholesterol in the blood with related hyperlipidemic disease states.
A condition which is associated with elevated levels of cholesterol, phospholipids, and/or triglycerides in mammals is commonly referred to as hyperlipidemia (i.e. as used herein, reference to hyperlipidemia is intended to be inclusive of both hypercholesterolemia and hypertriglyceremia, and hence, compounds having a hypolipidemic effect will exhibit activity to lower cholesterol and/or triglyceride lipid levels). Hyperlipidemia can lead to serious health problems such as artherosclerosis which may give rise to other cardiovascular disease states. Lipids occur in the blood mainly as cholesterol and triglycerides, with smaller amounts of phospholipids, fatty acids and fatty acid esters. While free fatty acids are bound to plasma albumin, the other lipids form complexes with proteins called lipoproteins. These differ in composition, size and density and include very low density lipoprotein (VLDL), low density lipoprotein (LDL) and high density lipoprotein (HDL) depending on the specific gravity of the apoprotein components of the fraction. Medical evidence points to the VLDL and LDL fractions as being associated with atherosclerosis. In contrast, the HDL fraction appears to carry cholesterol from the walls of the blood vessels to the liver where it is processed and excreted in the bile. As hyperlipidemic states increase in atherosclerosis the VLDL and LDL cholesterol increases and HDL cholesterol decreases. Effective hypolipidemic agents need to reverse this ratio since clinical data indicate that high HDL cholesterol and low LDL cholesterol protects man from myocardial infarctions. Thus, it is highly desirable to treat mammals afflicted with hyperlipidemia so as to lower cholesterol content of the VLDL and LDL fractions and increase the cholesterol content of HDL fraction.
Commercially available agents include nicotinic acid derivatives, clofibrate, cholestyramine, and cholestipol. A number of compounds have been proposed for the treatment of hyperlipidemia in mammals. Examples include U.S. Pat. No. 4,499,303 which describes the use of a novel class of N-benzylsulfamates, N-benzoylsulfamates, and benzoylsulfonamides as useful hypolipidemic agents. U.S. Pat. No. 4,395,417 proposes the use of cyclic imides, diones, reduced diones and analogs as useful hypolipidemic agents. Also orotic acid has been shown to decrease the plasma lipid level in rats. I. H. Hall et al., J. Pharm. Sci., 74, 759-64 (1985); I. H. Hall, G. H. Cocolas and W. L. Williams, Jr., J. Pharm. Sci., 73, 18-20 (1984).
U.S. Pat. No. 4,639,444 describes 3,5-dialkyl-4,6-diaryltetrahydro-2H-1,3,5-thiadiazine-2-thione derivatives as useful hypolipidemic agents. U.S. Pat. No. 4,681,893 teaches that certain trans-6-[2-(3- or 4-carboxamido-substituted pyrrol-1-yl)alkyl]-4-hydroxypyran-2-ones and their ring opened acids are potent hypolipidemic agents. Likewise, U.S. Pat. No. 4,351,844 describes hypocholesterolaemic lactone compounds and their free acids which are derived from the natural fermentation product mevinolin. More recently, the control of hyperlipidemia through the use of a class of 4-pyrimidinecarboxylic acids has been described by Hall et al., J. Pharm. Sci. 74, 759 (1985).
In spite of the numerous compounds and methods which have been proposed for the control of hyperlipidemia, the need remains for drugs having enhanced lowering effect on levels of certain lipoprotein lipids in the serum.
Accordingly, the present invention provides a class of hypolipidemic compounds which, when administered to mammals provide for a significant increase of the cholesterol content of the HDL fraction coupled with a desirable reduction of the cholesterol of the LDL fraction. Furthermore, the triglyceride and neutral lipid content of the VLDL fraction, which carries these lipids to the tissues from the liver, are markedly reduced.